Various analytical procedures and devices are commonly employed in flow-through assays to determine the presence and/or concentration of analytes that within a test sample. For instance, immunoassays utilize mechanisms of the immune systems, wherein antibodies are produced in response to the presence of antigens that are pathogenic or foreign to the organisms. These antibodies and antigens, i.e., immunoreactants, are capable of binding with one another, thereby causing a highly specific reaction mechanism that may be used to determine the presence or concentration of that particular antigen in a biological sample. Unfortunately, many conventional immunoassay assays encounter problems when used to measure test samples that possess a high analyte concentration. For instance, elevated levels of C-reactive protein (“CRP”) are sometimes indicative of certain diseases, such as heart disease. However, even normal blood samples may contain a high CRP concentration, often within the “milligrams per milliliter” range. Because most conventional immunoassays are designed to detect analyte concentrations in the “nanograms per milliliter” range, they will almost undoubtedly give positive results of the presence of CRP for all test samples, including those having a normal CRP concentration. This may be particularly troubling to consumers who are themselves performing the assay with a disposable device.
As such, a need currently exists for an assay device that is capable of detecting the presence of an analyte in circumstances where a “normal” test sample still contains relatively high levels of the analyte.